Digital Video Broadcasting (DVB) is a set of standards used for digital television broadcasting. The DVB standards include a number of different subsets. Satellite broadcasts can use variations of DVB-S, cable broadcasts can use DVB-C; terrestrial television can use variations of DVB-T, and digital terrestrial television for handhelds can use DVB-H or DVB-SH.
Current DVB-S broadband tuners are designed for receiving a relatively weak RF signal in the presence of multiple other signals including other channels or out of band interference. Many broadband DVB-S tuners receive channels between 950 MHz to 2150 MHz, down-converted from 12 GHz to 14 GHz by a low-noise block (LNB). Some systems have multiple antennas pointing to different satellites. This can result in the receiver needing to detect the desired signal in the presence of multiple channels and at a much lower level. Different cable lengths from LNB to indoor tuner and multiple down-converters further contribute to level imbalance between different received channels. As a result, the difference between a desired channel and an unwanted channel can be as high as 40 dB. Thus, a tuner should have a very good selectivity. Selectivity can be increased by filtering the undesired channel before reaching the demodulator.
Receivers with zero-IF and low IF have been developed to perform most of the filtering at low frequency rather than at RF. The RF stages, mixer and post mixer filters can have linearity constraints that can become problematic when multiple carriers with strong levels are present. Thus, filtering the signal in the RF front can be advantageous or even necessary. While it is possible to filter the unwanted signal before reaching the input of the tuner low-noise amplifier (LNA) this topology involves a series of passive external components that will take space, degrade noise figure and may not provide constant input impedance over frequency.
Aspects of the present invention allow for an integrated filter placed after the internal LNA capable of achieving front end selectivity, high linearity and sensitivity in the presence of unwanted strong signals. Other aspects of the present invention provide a reliable calibration architecture and method that increases performance for the filter.